System for driving a. d. c. electromagnet

ABSTRACT

A system for driving a DC electromagnet of the kind in which an armature is attracted by the magnetic action of current supplied to an electromagnetic winding, having an attraction starting circuit for generating a DC voltage for a predetermined period of time for completing the attraction of the armature, and an attraction-holding circuit for generating an intermittent voltage. After the voltage generated by the attraction starting circuit is applied to the electromagnetic winding to complete the voltage attraction of the armature, the intermittent voltage generated by the attraction holding circuit is solely applied to the electromagnetic winding for holding the armature in its attracted state. Thus, a large force of attraction is produced by a DC electromagnet having a small physical constitution and heat generated therein can be reduced.

United States Patent [72] Inventors Takaaki Kato Toyohashi-shi;

Mamoru Kawakubo, Kariya-shi, Japan [21] Appl.No. 847,558

[22] Filed Aug. 5,1969

[45] Patented May 18, 1971 [73] Assignee Nippon Denso Kabushiki Kaisha Kariya-shi, Japan [32] Priority Sept. 21, 1968 [54] SYSTEM FOR DRIVING A. D. C.

ELECTROMAGNET 7 Chins, 3 Drawing Figs. [52] US. Cl. 317/148.5, 317/123. 154 51 Int. Cl H02m 7/44, H02m 7/68 [50] FieldotSearch 317/123, 123 (CD), 148.5

[56] References Cited UNITED STATES PATENTS 1,915,566 6/1933 Younghusband 317/123 2,257,361 9/1941 Yorkey 317/123 2,858,485 10/1958 Seeger 317/123 3,116,441 12/1963 Gieffers..... 317/123 3,124,724 3/1964 Mihalek 317/123 3,205,412 9/1965 Winston 317/123 3,206,651 9/1965 Proulx 317/123 3,401,310 9/1968 Schaffersmann 317/123 3,461,375 8/1969 Nestler 317/123 Primary Examiner-Milton O. Hirshfield Assistant Examiner-U. Weldon Attorney-Cushman, Darby & Cushman ABSTRACT: A system for driving a DC electromagnet of the kind in which an armature is attracted by the magnetic action of current supplied to an electromagnetic winding, having an attraction starting circuit for generating a DC voltage for a predetermined period of time for completing the attraction of the armature, and an attraction-holding circuit for generating an intermittent voltage. After the voltage generated by the attraction starting circuit is applied to the electromagnetic winding to complete the voltage attraction of the armature, the intermittent voltage generated by the attraction holding circuit is solely applied to the electromagnetic winding for holding the armature in its attracted state. Thus, a large force of attraction is produced by a DC electromagnet having a small physical constitution and heat generated therein can be reduced.

Patented Ma 18, 1971 I 3,519,052

INVENTORS Takaa K; Ka

o o Ka akubo BY Mimi/0 Qmivmn ATTOR N F Y l SYSTEM FOR DRIVINGA. D. C. ELECTROMAGNET BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a driving system for a DC electromagnet in which an armature is attracted by the magnetic action of current supplied to an electromagnetic winding.

2. Description of the Prior Art In a conventional DC electromagnet, it is necessary to generate a magnetomotive force of an extremely large value in the electromagnetic winding of the magnet when a relatively large force of attraction is required. Prior well-known methods adapted for this purpose include a method of increasing the number of turns the electromagnetic winding while fixing the magnitude of the current and a method of increasing the magnitude of the current while fixing the number of turns of the electromagnetic winding. However, the former method is defective in that the space occupied by the electromagnetic winding increases resulting in a large physical constitution of the electromagnet. While the latter method is advantageous over the former method in that .a smaller space is occupied by the winding, it has such a defect that the increased current results in an increase in the power consumption and hence in a larger quantity of heat is generated thereby and therefore some means for cooling must be provided to dissipate the heat.

SUMMARY OF THE INVENTION It is a primary object of the present invention to provide a system for driving a DC electromagnet of the kind in which an armature is attracted by the magnetic action of current supplied to an electromagnetic winding, said system comprising an attraction starting circuit for generating a DC voltage for a predetermined period of time for completing the attraction of the armature, and an attraction-holding circuit for generating an intermittent voltage so that, after the DC voltage generated by said attraction starting circuit is applied to the electromagnetic winding to complete the attraction of the armature, the intemtittent voltage generated by said attraction holding circuit is solely applied to the electromagnetic winding for bolding the armature in its attracted state.

According to the present invention, a strong magnetometive force can be generated in the electromagnetic winding for the attraction of the armature without increasing the number of turns of the electromagnetic winding, and after the armature is once attracted, the amiature can be held in its attracted state without increasing the power consumption in the electromagnetic winding, hence keeping the heat generated to a nunimum.

BRIEF DESCRIPTION OF THE DRAWING FIG. 11 is an electrical connection diagram of an embodiment of the DC electromagnet driving system according to the present invention and a longitudinal sectional view showing the mechanical structure of the DC electromagnet.

FIGS. 20 and 2b are schematic representations of voltage wavefomis applied to the solenoid of the DC electromagnet.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a DC electromagnet is generally designated by the reference number i and includes a hollow tubular guide member 2 having a closed bottom, a spring 3 having one end thereof anchored to the bottom 2a of the guide member 2, and an armature 4 slidably received in the guide member 2 so as to be normally urged in one direction by the force of the spring 3. An abutment member 5 is provided at the open end 2b of the guide member 2 so that the armature 4 may not project from the guide member 2 by being urged by the resiliency of the spring 3. An electromagnetic winding 6 is wound around the guide member 2 and has two voltage application temtinals 6a and 6b. A yoke 7 of U-shaped section surrounds the electromagnetic winding 6 for establishing a magnetic circuit. Reference numeral b designates an attraction starting circuit which includes a monostable multivibrator 9. The monostable multivibrator 9 is constituted by transistors 10 and I1, resistors l2, 13 I4 and i5, and a capacitor l6. A transistor 17 has its collector connected to the voltage application terminal 6a of the electromagnetic winding 6, its emitter grounded and its base connected through a resistor I8 to the collector of the transistor ll in the monostable multivibrator 9. A trigger pulse generator 19 is constituted by a re- I sistor 20, a capacitor 21 and a diode 22. A transistor 23 is provided to drive the trigger pulse generator 19, and a load resistor 24 is connected to the collector of the transistor 23.

Reference numeral 25 designates an attraction-holding circuit which includes an astable multivibrator 26. The astable multivibrator 26 is constituted by transistors 27 and 18, resistors 29, 30, 3i and 32, and capacitors 33 and 34. A transistor 35 has its collector connected to the voltage application terminal 6a of the electromagnetic winding 6, its emitter grounded and its base connected through a resistor 26 to the collector the the transistor 27 in the astable multivibrator 26. A transistor 37 has its collector connected to the emitter of the transistor 28, its emitter grounded and its base connected to a stepped voltage application terminal 38 together with the base of the transistor 23. A diode 39 is connected across the voltage application terminals 6a and 6b in parallel relation with the electromagnetic winding 6. A power source or storage battery 49 has its positive electrode connected to the voltage application terminal 61) and its negative electrode grounded. In FIGS. 2a and 2b, the horizontal axis represents time t and the vertical axis represents voltage V applied to the electromagnetic winding 6.

Operation of the system according to the present invention having the structure described above will now be described in detail.

In the state in which no stepped voltage is applied to the stepped voltage application terminal 38 and both the transistors 23 and 37 are in their cutoff state, no trigger pulse is applied from the trigger pulse generator 19 to the monostable multivibrator 9 and therefore the monostable multivibrator 9 is in its quiescent state in which the transistor 10 is in its cutotf state while the transistor 11 is in its conducting state. Thus, no input voltage is applied to the base of the transistor 17 and the transistor 17 is in its cutoff state. Further, the astable multivibrator 26 is in its quiescent state in which the transistor 27 is in its conducting state while the transistor 28 is in its cutoff state. Thus, no input voltage is applied to the base of the transistor 35 and the transistor 35 is in its cutoff state. Therefore, no voltage is applied to the electromagnetic winding 6 and the armature 4 remains to pressed against the abutment member 5 by the force of the spring 3.

When now a stepped voltage is applied to the stepped voltage appiication terminal 38 so as to attract the armature 4 against the force of the spring 3, both the transistors 23 and 37 are urged to their conducting state and a negative trigger pulse is applied from the trigger pulse generator R9 to the monostable multivibrator 9. Thus, the state of the monostable multivibrator 9 is inverted so that the transistor 10 is urged into its conducting state and the transistor 11 is urged to its cutoff state. Time T during which the transistor 11 is kept in its cutofr" state is determined by the resistance of the resistor 13 and the capacity of the capacitor 16. Thus, the transistor 17 is kept in its conducting state for the limited time T described above.

A DC voitage is applied for a limited fixed time T to the electromagnetie winding 6 as shown in H6. 2a to supply current from the storage battery 40 to the electromagnetic winding 6 through the transitor 17. Magnetic flux produced by the electromagnetic winding 6 passes through the magnetic circuit shown by the broken line in FIG. it and the armature 4 is attracted by the magnetic action toward the bottom 2a of the guide member 2 against the force of the spring 3 until it rests at a position which substantially no air gap exists between it and the yoke 7. Attraction of the armature 4 is completed within the above-specified time T. After the armature 4 has been attracted toward the bottom 2a of the guide member 2 in the manner described above, substantially no air gap exists between the armature 4 and the yoke 7 resulting in a very low magnetic reluctance. Thus, in order to obtain the same magnetic flux as when there is an air gap between the armature 4 and the yoke 7, the magnetomotive force that must be produced in the electromagnetic winding 6 can be quite small.

On the basis of such a theory, the armature 4 can be kept in its attracted state after it has been attracted toward thebottom 2a of the guide member 2. More precisely, when the transistor 17 is kept in its conducting state by the output from the monostable multivibrator 9, the astable multivibrator 26 is repeatedly inverted from its quiescent state due to the fact that the transistor 37 is is connected in series with the transistor 28 is in its conducting state. Thus, the astable multivibrator 26 generates a pulse which is dependent upon the resistance of the resistor 30 and the capacity of the capacitor 33 or the resistance of the resistor 31 and the capacity of the capacitor 34. As a result, the transistor 35 repeats its conducting and cutoff state in synchronism with the pulse. However, the emitter and collector of the transistor 35 are at the same potential during the time T because transistor 17 is in its conducting state. Thus, the transistor 35 does not make intermittent operations during the time T, but only after the time T. Accordingly, after the attraction of the armature 4 is completed, that is, after time T, an intermittent voltage as shown in FIG. 2b is applied to the electromagnetic winding 6 and has a mean value which is lower than the DC voltage shown in H6. 2a. It will be recalled in this connection that the magnetic reluctance of the magnetic circuit is reduced once the armature 4 has been attracted toward the bottom 2a of the guide member 2. Thus, application of the intermittent voltage with a small mean current value to the electromagnetic winding 6 can produce in the electromagnetic winding 6 a magnetomotive force which is sufficient to retain the armature 4 in its attracted state. It will be understood that the armature 4 can continuously be kept in its attracted state with a small power consumption.

The diode 38 is connected across the voltage application terminals 6a and 6b of the electromagnetic winding 6. Thus, when the voltage applied to the electromagnetic winding 6 is interrupted at a fast rate, current flows through closed circuit formed by the electromagnetic winding 6 having an inductance and the diode 39. Hence, the current flowing through the electromagnetic winding 6 is continuous and not intermittent. The means value of the current flowing through the electromagnetic winding 6 in this case can be set at a freely selected small value compared with the value of the current flowing through the electromagnetic winding 6 in the conducting state of the transistor 17 by suitably varying the rate of intermission within a range in which the armature can be kept in its attracted state.

We claim:

l. A system for driving a DC electromagnet of the kind in which an armature is attracted by the magnetic action of a current supplied to an electromagnetic winding, said system comprising output tenninal means adapted to be connected to said winding,

attraction-starting circuit means connected to said terminal means for generating a DC voltage continuously for a predetermined period of time,

attraction holding circuit means connected to said terminal means for generating an intermittent voltage, and

means, including a connectionbetween aid starting and holding circuit means, for mutually exclusively applying said DC and intermittent voltages in that order to said output terminal,

the arrangement being such that upon connection of the output terminal means to said winding, the DC voltage generated by said attraction-starting circuit means is first applied to the electromagnetic winding to effect the attraction of the armature, after which the intermittent voltage generated b said attraction-holding circuit means 18 solely applle to the electromagnetic winding for holding the armature in its attracted state.

2. A system as in claim 1 including input terminal means connected commonly to said starting and holding circuit means for receiving a common trigger signal by which said circuit start to operate simultaneously, said connection between said starting and holding circuit means being such that the said inten'nittent voltage is suppressed and not applied to said output terminal means while said DC voltage is generated and applied thereto during said predetermined time.

3. A system as in claim 2 wherein each of said starting and holding circuit means includes a respective output valve referenced to a predetermined level of voltage so that when said starting circuit means is generating said DC voltage its output valve effectively shorts the said intermittent voltage to said predetermined voltage level.

4. A system as in claim 1 wherein said output terminal means includes two terminals and said system further includes means connected across said terminals for causing the current flowing through said winding, when the output terminals are connected thereto, to be continuous while the voltage causing that current is the aforesaid intermitterit voltage.

5. A system as in claim 4 wherein said continuous currentcausing means includes a diode.

6. A system as in claim I wherein said attraction-starting circuit means includes a monostable multivibrator and a switching elementconnected between said multivibrator and said output terminal means to control the application of voltage thereto in response to operation of said multivibrator,

said attraction-holding circuit means including an astable multivibrator and a second switching element connected between said astable multivibrator and said output terminal means for switching voltage thereto in response to operation of said astable multivibrator in the absence of switching by said first-mentioned switching element of voltage from said monostable multivibrator.

7. A system as in claim 1 including in combination therewith the said electromagnet and its winding and armature, said winding being connected across said output terminal means. 

1. A system for driving a DC electromagnet of the kind in which an armature is attracted by the magnetic action of a current supplied to an electromagnetic winding, said system comprising output terminal means adapted to be connected to said winding, attraction-starting circuit means connected to said terminal means for generating a DC voltage continuously for a predetermined period of time, attraction holding circuit means connected to said terminal means for generating an intermittent voltage, and means, including a connection between aid starting and holding circuit means, for mutually exclusively applying said DC and intermittent voltages in that order to said output terminal, the arrangement being such that upon connection of the output terminal means to said winding, the DC voltage generated by said attraction-starting circuit means is first applied to the electromagnetic winding to effect the attraction of the armature, after which the intermittent voltage generated by said attraction-holding circuit means is solely applied to the electromagnetic winding for holding the armature in its attracted state.
 2. A system as in claim 1 including input terminal means connected commonly to said starting and holding circuit means for receiving a common trigger signal by which said circuit start to operate simultaneously, said connection between said starting and holding circuit means being such that the said intermittent voltage is suppressed and not applied to said output terminal means while said DC voltage is generated and applied thereto during said predetermined time.
 3. A system as in claim 2 wherein each of said starting and holding circuit means includes a respective output valve referenced to a predetermined level of voltage so that when said starting circuit means is generating said DC voltage its output valve effectively shorts the said intermittent voltage to said predetermined voltage level.
 4. A system as in claim 1 wherein said output terminal means includes two terminals and said system further includes means connected across said terminals for causing the current flowing through said winding, when the output terminals are connected thereto, to be continuous while the voltage causing that current is the aforesaid intermittent voltage.
 5. A system as in claim 4 wherein said continuous current-causing means includes a diode.
 6. A system as in claim 1 wherein said attraction-starting circuit means includes a monostable multivibrator and a switching element connected between said multivibrator and said output terminal means to control the application of voltage thereto in response to operation of said multivibrator, said attraction-holding circuit means including an astable multivibrator and a second switching element connected between said astable multivibrator and said output terminal means for switchIng voltage thereto in response to operation of said astable multivibrator in the absence of switching by said first-mentioned switching element of voltage from said monostable multivibrator.
 7. A system as in claim 1 including in combination therewith the said electromagnet and its winding and armature, said winding being connected across said output terminal means. 